Stepper Motor Speed limited using MAX

[TCjr]

I'm using a PXI-7352 controller with a MID-7602 Stepper Power Drive to control one stepper motor with an encoder. I've been experimenting with various settings in MAX to try and increase the velocity, but the highest I can achieve is about 500 steps/sec. I've made numerous changes in the PID section but nothing seems to improve. Occasionally, when 500 steps/sec has been exceeded, it ramps up for a short time and then stalls for short time and then ramps up again and stalls. This process is repeat until the motor stops and falls short of the target position. Any suggestions or recommendations would be helpful.

Terry

[Brian_Beal]

PID settings aren't used for steppers.  What resolution do you have set on the drive.  In other words, 500 steps/sec equals how many revs/sec?  It sounds like you are exceeding the limits of your motor.  It stalls, then attempts a pull-in move, etc., until that max number of pull-in moves have been met.  Steppers do not have a good speed/torque curve.  Torque drops off rapidly the faster you go.

[TCjr]

Brian,

Thanks for responding. I have an encoder on the motor that has 4000counts/rev. I have added plantary gears to the output of motor to increase my torque. My microstep rate setting on the drive unit is "half step" which means I've set the Microstep Rate DIP Switches to 2.

I'm curious about something the motor can be wired in series or parallel. Its currently wired in series and I wondering if changing the wiring to parallel would give me additional speed.

tks, Terry

[Vivek_N]

Terry,

I think the series and parallel setting is with regard to connecting multiple motors in serial or parallel - with just one motor, I do not think this makes a difference. To ascertain this, I would just look at the manual for the motor.

Please check the maximum speed of the motor you have, and the Velocity Constraints setting under Trajectory Settings for the axis in MAX. I hope this helps. 

[Brian_Beal]

Terry-

Parallel winding wiring will give you more torque at higher speeds.  Series winding wiring will give you higher torque at low speeds.  Your drive only puts out 24VDC, and that will limit your top speed.  What is the model number of your motor?  A typical high-torque NEMA23 motor will have the torque fall off rapidly above about 5 revs/sec with a parallel winding(at 24VDC). 

[Brian_Beal]

Without knowing what motor you have, I am going to guess that a speed of 500 steps/sec=1.25 revs/sec.

[Buechsenschuetz]

Maybe your drive is in a resonance condition. When stepper motors drive only small loads or no load at all, under certain conditions they will give irregular movements. Sometimes they still move but oscillate at certain positions, sometimes they just oscillate, and when you use a feedback device, this may cause the system to stall since the control system detects an erraneous movement when the number of input pulses does not comply with the number of feedback pulses. Try to add some mechanical load with some more inertia to the motor shaft. Some stepper motor vendors sell special damping discs for their stepper motors.